A Test Method to Determine Expected GCL Porosity under Specific Site Conditions

摘要

Determination of the porosity and void ratio of porous shrink-swell materials under conditions experienced on-site is critical to understanding expected advective and/or diffusive flux. Porosity estimates for geosynthetic clay liners (GCLs) depend on subtle interactions within the pore spaces governed by a particular leachate flux processes. For clay based lining materials, such as geosynthetic clay liners or compacted clay, the effective porosity or void ratio depends on the effective stress, saturation conditions of the lining system and the interactions between the leachate and the clay, which impact flow path tortuosity. This paper will describe a test method to calculate the porosity of GCLs under specific conditions of effective stress and saturation. The GCLs used for this analysis consisted of powdered sodium bentonite encapsulated by needle-punching between nonwoven cover and woven carrier geotextiles. Total specimen thickness was measured in a large-scale direct shear box where normal stresses were applied with step-load motors up to 1000 kPa and changes in thickness of the GCL were recorded in real-time as the GCL hydrated and consolidated. Results indicate that the total void ratio of hydrated GCLs is essentially equivalent to that of the bentonite component only, because the bentonite fills all geotextile void spaces. At stresses as high as 1000 kPa, the geotextile fibres are compressed and the geotextile voids are absent. The interparticle voids in the bentonite trend toward zero. Thus, traditional methods to measure porosity and void ratio of GCLs will over-estimate the importance of the geotextile under high confining stresses.